Synergistic interactions among various ototraumatic agents have been shown to be of importance in determining the hearing loss in a number of industrial situations. The interactions between continuous and impulse noise and vibration and impulse noise will be studied using an experimental animal model (chinchilla). The rationale for these studies is that noise rarely exists as a sole hazard to hearing in many industrial and military work environments. Specific studies will include: (1) Long term combination noise exposures leading to a state of asymptotic threshold shift (ATS). The intensity and spectrum of both the impulse and bacground noise will be varied to provide a perspective on the noise parameters essential for the "interaction effect". (2) Using an ATS exposure paradigm, the influence of acceleration on the interaction of noise and vibration will be studied; and (3) Psychophysical tuning curves will be used to study changes in frequency selectivity resulting from some of the complex patterns of damage induced by the noise exposures. The final format of the data will include a comprehensive description of the noise exposure, a profile of the animal's hearing capability before and after the treatment and a detailed quantitative morphological analysis of the cochlea. Our problem for this research grant is to experimentally examine the factors that influence the interaction between vibration and various noise exposure paradigms. The potential for syngeristic interactions among the various physical agents is large, and for the most part unexplored. While standards cannot be developed to cover all situations, we should at least be cognizant of the various risks entailed under a variety of exposure conditions. The results will also provide some insights into the establishment of scientificatlly based noise exposure standards.